Ultrafine nanoparticles with organic–inorganic hybridization have essential roles in myriad applications. Over the past three decades, although various efforts on the formation of organic or inorganic ultrasmall nanoparticles have been made, ultrafine organic–inorganic hybrid nanoparticles have scarcely been achieved. Herein, a family of ultrasmall hybrid nanoparticles with a monodisperse, uniform size is synthesized by a facile thermo‐kinetics‐mediated copolymer monomicelle approach. These thermo‐kinetics‐mediated monomicelles with amphiphilic ABC triblock copolymers are structurally robust due to their solidified polystyrene core, endowing them with ultrahigh thermodynamic stability, which is difficult to achieve using Pluronic surfactant‐based micelles (e.g., F127). This great stability combined with a core–shell–corona structure makes the monodispersed monomicelles a robust template for the precise synthesis of ultrasmall hybrid nanoparticles with a highly uniform size. As a demonstration, the obtained micelles/SiO2 hybrid nanoparticles display ultrafine sizes, excellent uniformity, monodispersity, and tunable structural parameters (diameters: 24–47 nm and thin shell thickness: 2.0–4.0 nm). Notably, this approach is universal for creating a variety of multifunctional ultrasmall hybrid nanostructures, involving organic/organic micelle/polymers (polydopamine) nanoparticles, organic/inorganic micelle/metal oxides (ZnO, TiO2, Fe2O3), micelle/hydroxides (Co(OH)2), micelle/noble metals (Ag), and micelle/TiO2/SiO2 hybrid composites. As a proof of concept, the ultrasmall micelle/SiO2 hybrid nanoparticles demonstrate superior toughness as biomimetic materials. A library of ultrasmall hybrid nanoparticles with great uniformity, monodispersity, and tunable shell thickness is successfully synthesized by a facile thermo‐kinetics‐mediated copolymer monomicelle approach. This monomicelle with a solidified polystyrene core has ultrahigh thermodynamic stability. Combined with a unique core–shell–corona structure, this monomicelle is a very general template to synthesize various ultrasmall, monodispersed hybrid nanoparticles with excellent uniformity.